How to get rid of thrips on garden and indoor plants

Silver streaks on the leaves, and something too small to see

Thrips are under 2mm long and they move fast, so most people work out they have them from the damage rather than from the insect. The tell is a silvery or speckled streaking on the leaf where the thrips have rasped the surface and drunk what came out, and alongside it a scatter of tiny black specks, which are droppings. Badly hit leaves come out distorted and the new growth looks puckered.

Confirm it before you treat anything

Hold a sheet of plain white paper under the leaf and give the plant a firm shake. Thrips drop off and you'll see them scurrying about on the paper as thin dark slivers, and once they're on white you can see them easily enough. Doing this first matters, because silver streaking on a leaf can also be mites or sun damage, and each of those wants a different answer.

The soap spray, and how to use it without burning the plant

A weak soap solution kills soft bodied insects by stripping the waxy coating off them so they dry out, and it costs almost nothing. Mix about 1 teaspoon of a plain soap into 1 litre of water. Use a pure soap rather than a dishwashing liquid full of degreasers and fragrance, because the additives are what damages foliage.

Then spray it properly. Get the undersides of the leaves, which is where thrips sit, and do it in the early morning or the evening rather than in hot sun, since soap plus heat is how you scorch a plant you were trying to save. Test it on a few leaves and wait a day before you do the whole plant, because some things take it badly and it's better to find out on one leaf than on all of them. You'll need to repeat it every 5 to 7 days for a few rounds, as the spray doesn't touch the eggs and a new lot hatches out behind it.

When soap isn't enough

For a heavier infestation there are horticultural oils and ready to use sprays that'll do the job with less repetition. Whatever you use, spot treat the affected plant rather than dousing the whole bed, and spray at dusk when fewer beneficial insects are moving, because the predators that eat thrips are the ones keeping the next outbreak small.

Making the place less attractive to them

• Keep the predators around. Lacewings and predatory mites work through thrips steadily, and a garden that gets sprayed broadly loses them first.
• Clear the weeds along the fence line. Thrips breed up in weedy ground and move into the garden from there, so that strip you've been ignoring is often where it starts.
• Watch new plants. Thrips very often arrive on something you brought home, so keep a new plant away from the others for a fortnight and have a look at it before it joins them.
• Don't over-feed. Soft sappy growth from heavy nitrogen is exactly what thrips prefer, so an under-fed plant is sometimes the better defended one.

Indoors is a bit different

House plants have no predators working for them, so an indoor infestation keeps going until you stop it. Wipe the leaves down, treat with the soap spray the same way, and keep the affected plant separate from the rest of the collection until you've had a clear couple of weeks.

And if you've had a look at the paper and you're still not sure what's on it, bring a leaf into the shop in a bag. Working out what it is takes a minute at the counter and it saves you buying the wrong spray twice.

Shop related products

• Brunnings White Oil RTU 1L. A horticultural oil, ready to use, for sap suckers on leaves.
• Multicrop EcoPest Oil Insect Spray. The softer option when you want to keep the good insects.
• Multicrop Pyrethrum Long Life Insect Spray 1L. For a heavier hit on a plant that's getting away.
• Brunnings Bug and Fungus Kill RTU 1L. Where there's a fungal problem riding along with the insects.

Did you know we stock garden sprayers in the shop, from a 1 litre pressure sprayer up to a 12 litre knapsack, which is what you want if you're mixing your own soap solution. They aren't on the website, so ring us on (08) 8536 4333 to check what's on the shelf.

The garden centre carries the sprays and the gear that goes with them, so have a look through the pest control range or the wider garden range.

Read next

• Which garden insects are worth keeping around
• How to control garden pests without hurting bees
• How to clean houseplant leaves, and why it matters

I'm firmly of the view that half of pest control is working out what you're actually looking at, and I'm still wrong about that often enough to keep the paper trick handy.

Cheers,
Candeece